Lipoxygenases are membrane-bound ubiquitous enzymes which catalyze the hydroperoxidation of polyunsaturated fatty acids in the first step of fatty acid metabolite synthesis. Products of this pathway are found as signal molecules, involved in growth and development regulation, in senescence, and in response to pathogen invasion and wound stress (Rosahl (1996) Z. Naturforsch. [C] 51:123-138). Lipoxygenases with different specificities, subcellular location, and tissue-specific expression patterns have been identified in several plants including rice, barley, soybean, tomato, cucumber and potato.
Many lipoxygenase cDNAs have been identified in barley, but two isozymes have been characterized, lipoxygenase 1 and 2. The amino acid sequence of proteolytic fragments from the barley isozyme 1 are identical to the predicted partial amino acid sequences from the potato IoxA and the rice L2. The methyljasmonate-induced 100 kDa lipoxygenase has been characterized as a barley isozyme 2 (Voros et al. (1998) Eur. J. Biochem. 25:36-44). As a response to wounding, the potato Lox1 is expressed mainly in tubers and roots while Lox2 is expressed almost exclusively in leaves and Lox3 in leaves and roots. Linoleic acid is preferentially utilized as a substrate by Lox1 which produces mainly 9-hydroxyperoxides. Utilizing the same substrate, the major product of Lox2 and Lox3 is the jasmonic acid precursor 13-hydroperoxilinolenic acid (Royo et al. (1996) J. Biol. Chem. 271:1012-1019). Fungal infection of plants has allowed the identification of lipoxygenases which are induced upon microbial treatment such as the rice lipoxygenase L2 which introduces a molecular oxygen into the C-13 position of linoleic and linolenic acid (Peng et al. (1994) J. Biol. Chem. 269:3755-3761).
Because lipoxygenases play so many different roles and have different specificities, knowing the amino acid sequences for lipoxygenases present in different plants will allow the understanding of plant development and wound response.